1. Field of the Invention
The present invention relates to automotive component parts. More specifically, the present invention relates to the efficient fabrication of automotive suspension parts by first extruding portions thereof, and subsequently joining these various sections to form the completed automotive parts.
2. Description of the Related Art
In any given automobile design, countless diverse components are operatively coupled together to create a sophisticated, high performance machine. Certain components are relatively simple in their design, but can always be improved. Further, the way these parts are fabricated can similarly be improved to provide additional advantages and features. For example, design improvements can continually be made to improve the structural integrity of the product itself. These design improvements may involve how internal component stresses can be better handled, or may allow for manufacturing efficiencies to be improved. Furthermore, weight reduction can be realized through these design improvements.
Many components have fairly straight forward design criteria based upon their purpose, function, and relationship with other components. One such component is the link arm, or link rod, that is used in suspension systems. A common link rod design is made up of a steel tube that is welded between a pair of steel eyes. Each eye is fabricated from a steel ring having a wall thickness sufficient to provide the necessary structural performance. To join these components together, the eyes are welded to each end of the steel tube. Generally a gas metal arc weld (GMAW) is utilized to achieve the necessary bonding characteristics.
As is obvious, any components, such as the link rod, which carry loads in a vehicle must easily withstand all loads without the possibility of failure. Due to the shape, design and interconnection of the various components that make up a typical link arm, a majority of the load stress is concentrated at the weld area. It is normally undesirable to have significant loads carried by welded joints due to the possibility of irregularities and inconsistencies in the weld. Geometrical changes are produced at weld joints which cause stress concentration areas reducing product performance. Significant changes in the geometry and metallurgy at the welded joints create a possibility for product breakage or failure. The location of weld joints is consequently a very important design consideration.
The use of designs which include a significant number of welded components are further undesirable due to problems in maintaining tolerances. More specifically, it is difficult to maintain precise tolerances among components when undergoing welding operations due to the substantial heat and material stresses that are introduced through the welding process, causing expansion, bending, bowing and other misalignment concerns. In the specific case of the link arm, maintaining exact dimensions and alignment between the two eyes becomes difficult during the welding processes.
Another consideration in today""s market is that vehicles are becoming increasingly modular, which requires flexibility among the various components. Naturally, the various components must meet certain physical requirements which are dictated by their application. For example, the link arm is limited to certain lengths and overall dimensions which must possess sufficient structural integrity to withstand certain predetermined axial load levels. Various vehicles may require similar characteristics from its link arms, but may have different length specifications and packaging constraints. Unfortunately, two separately fabricated parts are typically necessary to meet this need.
In addition to all of the structural and strength requirements, weight and cost are also concerns. Any reduction in weight of various component parts results in similar weight reductions for the overall vehicle weight. Naturally, this will result in improved vehicle operating costs, power requirements, etc. Cost concerns are overcome by manufacturing efficiencies which help to reduce overall production costs, and final component part costs as well. Consequently, cost and weight reductions are continual goals when designing any particular component. Therefore, there exists a need to provide an improved link arm meeting the predetermined structural requirements while meeting or exceeding current efficiencies in cost and production, while allowing for a reduction in weight.
The present invention seeks to produce a link arm with a flexible design for use in a vehicle suspension system which has a need for a reduction in weight. Specifically, the present invention reduces the overall weight and manufacturing complexity of the link arm or rod while maintaining a competitive cost. In achieving these weight and cost savings, the design of the present invention provides either equal or improved levels of structural reliability.
To achieve the weight reduction desired, the link arm of the present invention is comprised entirely of aluminum (or other similar light weight materials). In the case of the extruded aluminum link rod of this present invention, weight reductions of thirty percent or more from a similarly sized and shaped traditional steel link arm can be realized. However, replacing steel with aluminum creates additional complications. That is, it is generally not practical to join a tubular aluminum rod to a pair of aluminum rings or eyes as was the approach in the steel link arm. This impracticality is due to differing material strengths and weld characteristics, with the welds having less than half of the strength of the base material. As previously discussed, the transition from the small diameter steel tube to the large diameter eye concentrates a majority of the load stress in the weld area. Aluminum components of this configuration would not easily meet all of the necessary manufacturing and design requirements of the end product while producing a weight reduction.
To achieve the desired weight reduction by utilizing aluminum, the configuration of the link arm of the present invention is quite distinct from its steel counterparts. Furthermore, to produce such an aluminum link arm in a cost effective manner, a new manufacturing process is utilized.
When viewed from the top (or bottom), the completed aluminum link arm has a generally rectangular configuration. When viewed from the side, a substantial portion of the interior or center section is also rectangular in configuration. Towards each end of the link arm, a transition area begins to taper outward and split, forming a pair of transition arms. An area between the transition arms is hollow. The transition arms terminate in an integrally connected hollow aluminum eye. Again, the entire link arm is fabricated from aluminum achieving a significant reduction in weight. As previously mentioned, other lightweight materials could also be used to fabricate the product, so long as they meet the material and performance requirements outlined below.
To form the aluminum link arm, aluminum is fed through an extrusion press to form components having the desired cross-sectional shape. Several options exist as to the exact number of extruded components required to form a completed link arm. While theoretically possible to form the entire link arm in a single extrusion process, this approach is not practical due to the length of a typical link rod. At present, it is not cost effective to utilize an extruder capable of producing a single extrusion link arm due to the higher cost and poor tolerances of larger extrusions. Thus, for practical purposes the aluminum link arm of the present invention is formed from at least two extruded components.
In a first embodiment, the extruded component forms one-half of the completed aluminum link arm. As further outlined below, these extruded components are then friction stir welded and subsequently cut to size after welding. The welded extrusion assembly has a length much larger than the eventual width of a single completed link arm component. To join the extrusions they are first paired side by side and then fed through a friction stir welder. Each single extrusion forms one side of the completed product including the above-described eye and a pair of transition arms which lead to a generally rectangular section which terminates in an edge for friction stir welding. By abutting the friction stir welding edge of two such extrusions and then welding them, the resulting cross-sectional configuration is that of the aluminum link arm.
By joining two extrusions through the friction stir welding process, no additional material is added (thus preventing additional weight). Further, the friction stir weld process produces welds that are near base material strength, or two times the strength of gas metal arc welds. The welds are thus more than capable of withstanding the loads exerted upon a completed link arm. Since the remainder of the link arm is integrally formed through the extrusion process, there is no joint or weld that interconnects the main body of the arm to the eye portions. Stated alternatively, the friction stir weld is not placed in the same location as that of the steel Gas Metal Arc welded tubular link rod.
In a second possible embodiment, three separate extrusions are used to form a completed link arm. The first two extrusions are similar to those produced in the first embodiment. That is, a hollow eye is produced which is integrally connected to a pair of transition arms that tapers into a somewhat rectangular area that terminates in an edge for friction stir welding. One could simply connect these two extrusions together and produce what amounts to a shortened aluminum link arm. However, in this embodiment a third extrusion or plate is utilized. The third piece is a generally rectangular member having a cross-sectional height equal to the cross-sectional height of the extrusions containing the eye and a predetermined length. The extruded components are aligned so that the rectangular section is disposed between the two extrusions having hollow eyes. Specifically, the edges are aligned and again are joined through a friction stir welding process. Thus, by adjusting the dimensions of the center-piece, the overall length of the link arm can easily be modified.
The combination of extruded component parts and friction stir welding provides a very efficient manufacturing process. The extrusion process is relatively simple and inexpensive. The friction stir welding process is efficient and provides high integrity joints. What results is an aluminum link arm having a weight reduction of at least one-third of its steel counterpart while maintaining or exceeding the structural viability of the steel counterpart. Importantly, the total costs to produce the aluminum link arm is low and is comparable with that of producing steel link rods due to the elimination of manufacturing processes.
As is known, friction stir welding occurs by plunging a rotating tool into the metal of two abutted components. The rotating tool is then moved along the seam between these two components. As this occurs, the material is plasticized and mixed essentially forming a bond between the two components. The depth of the tool is selected to correspond to the depth of a seam. In the present invention, the rotating tool passes along the seam created when the two extrusions are aligned side by side. By having the rotating tool travel the entire length, a strong and consistent weld is created along the entire length of the seam. Friction stir welding operations may be performed on one or both sides of the component, depending upon the desired weld characteristics. In another variant, two friction stir welders can be used, each acting along opposite sides of the same seam simultaneously. The friction stir weld tools plunge into the two abutted components, one from the top and the other from the bottom.
Friction stir welding is an important aspect of the present invention due to the resulting consistent, high integrity and quality bond. As previously mentioned, an extremely strong weld occurs between the various components. Additionally, friction stir welding requires minimal amounts of heat as compared to other welding processes, and consequently avoids many disadvantages of classical welding processes. That is, residual stresses and distortion generally caused by the heat utilized in traditional welding processes is significantly reduced through the use of friction stir welding. Thus, friction stir welding accommodates the production of more precise and easily controlled parts because distortion is not inherently created.